Dual effects of dopamine in rat adrenal glomerulosa cells

Differences between the growth regulatory pathways in primary rat adrenal cells and mouse tumor cell line

In this study, DNA synthesis, phosphorylation of ERK1/2 and CREB proteins, as well as induction of c-Fos protein, were examined in rat adrenocortical, glomerulosa and fasciculata/reticularis cells, as well as in the Y1 cell line. We found that FGF2 was mitogenic only in glomerulosa cells and although ACTH did not activate ERK1/2, it did activate CREB protein, indicating efficient transduction of signals initiated in the ACTH receptors of rat adrenocortical cells. The FGF2 activated ERK1/2 in rat adrenal cells by a mechanism that might be modulated by upstream PKA pathway phosphorylation of MEK and despite the nonmitogenic effect of ACTH on rat adrenal cells it effectively induces c-Fos protein. The results presented herein describe distinct differences between the ACTH and FGF2 signal transduction mechanisms seen in adrenocortical cells and those observed in the Y1 cell line, indicating that, in vitro, ACTH blockage of the mitogenic effect occurs in normal adrenal cells after induction of c-Fos protein.

A Ras-dependent chloride current activated by adrenocorticotropin in rat adrenal zona glomerulosa cells

In the present study, we report that ACTH induces a transient chloride current. The lack of correlation between ACTH-induced cAMP production and amplitude of the Cl- current, as well as the absence of stimulation by forskolin or 8Br-cAMP indicated that the ACTH-induced current was not cAMP-dependent. We explored the possibility that one or several elements of the Ras/Raf MAPK cascade were involved. Indeed, we found that ACTH at 10(-10) M induced activation of Ras. Inhibition of the current by QEHA peptide, a Gbetagamma sequestrant, demonstrated that Gbetagamma subunits transduced the message. Blockage of the Ras activation using an inhibitor of farnesyl transferase (BZA-5B) or the monoclonal antibody H-Ras(259) abrogated the current. Moreover, the addition of Ras-GTPyS in the pipette medium gave rise to the Cl- current. Treatment of the cells with BZA decreased the aldosterone secretion induced by 10(-10) M ACTH but not that induced by 10(-8) M ACTH, confirming the involvement of Ras in steroid secretion. We conclude that ACTH triggers a Cl- current through the activation of the Ras protein by Gbetagamma subunits. This current, activated at physiological ACTH concentrations (1 to 100 pM) where cAMP production is very low, could play a significant role in aldosterone production.

Prompt recovery of damaged adrenal medullae induced by salinomycin

The morphologic changes in the adrenal medullae of rats treated with an ionophore antibiotic, salinomycin, are described. Male rats of approximately 7 wk of age were treated orally with a single dose of salinomycin at 80 mg/kg body weight. Following this treatment, the adrenal glands were examined, using immunohistochemistry, for neurofilament, laminin, fibronectin, and S-100 protein; the glands were also examined using transmission electron microscopy. One hour after the treatment, a karyopyknosis was observed in the clusters of affected chromaffin cells in which the neurofilament, laminin, and fibronectin were present. The lesions became progressively conspicuous between hours 5 and 10. Ultimately, the outcome was cell lysis. Five hours after salinomycin treatment, unaffected chromaffin cells strongly stained to tyrosine hydroxylase. At 10 hr, new chromaffin cells, which were irregular in shape with electron-dense cytoplasm (dark cell), that were strongly stained for tyrosine hydroxylase appeared at the basement membrane site of the necrotic clusters, and these cells contained very few immature catecholamine granules of less than 80 nm. At 17 hr, the catecholamine granules increased in number and size to about 200 nm. The newly formed chromaffin cells grew within the clusters to fill in the medulla by 24 hr, and cytoplasmic granules progressively increased in number and size. The interstitial tissue was seen to be edematous at 5 hr. New capillaries were found in the adrenal medullae of both control and salinomycin-treated rats. The protruding chromaffin cells (protruding cells), which we previously described in normal rats, were also observed in salinomycin-treated rats, which suggests that holocrine secretion is performed in the adrenal medullae. The results indicated that the rat adrenal medullae have the ability to make a rapid recovery after an insult by salinomycin.

Inhibition of the T-type Ca2+ current by the dopamine D1 receptor in rat adrenal glomerulosa cells: requirement of the combined action of the G betagamma protein subunit and cyclic adenosine 3',5'-monophosphate

Modulation of ionic Ca2+ currents by dopamine (DA) could play a pivotal role in the control of steroid secretion by the rat adrenal glomerulosa cells. In the present study, we report that DA decreases the T-type Ca2+ current amplitude in these cells. The use of pharmacological agonists and antagonists reveals that this effect is mediated by activation of the D1-like receptors. Modulation by cAMP is complex inasmuch as preincubation of the cells with 8-Br-cAMP or the specific adenylyl cyclase inhibitor, 2',3'-dideoxyadenosine, have no effect per se, but prevent the DA-induced inhibition. The inhibitory effect of DA was abolished by addition of GDPbetaS to the pipette medium but not by pertussis toxin. If a cell is dialyzed with medium containing G alpha(s)-GDP, the inhibitory effect is reduced and cannot be recovered by the addition of GTPgammaS, indicating that the alpha(s) is not involved, but rather the betagamma-subunit. Indeed, DA-induced inhibition was mimicked by G betagamma in the pipette and 8-Br-cAMP in the bath. Similarly, G betagamma release from the activation of the AT1 receptor of angiotensin II did affect the current amplitude only in the presence of 8-Br-cAMP in the bath. The mitogen-activated protein kinase cascade, which can be activated by receptors coupled to Gs, was not involved as shown by the lack of activation of p42mapk by DA and the absence of effect of the mitogen-activated protein kinase inhibitor, PD 098059, on the DA-induced inhibition. Because the binding of G betagamma-subunits to various effectors involves the motif QXXER, we therefore tested the effect of the QEHA peptide on the inhibition of the T-type Ca2+ current induced by DA. The peptide, added to the medium pipette (200 microM), abolished the effect of DA. We conclude that the presence of the G betagamma and an increase in cAMP concentration are both required to inhibit the T-type Ca2+ current in rat adrenal glomerulosa cells.

Localization of dopamine D1A receptor protein and messenger ribonucleic acid in rat adrenal cortex

Pharmacological, physiological, and autoradiographic studies have suggested the presence of dopamine receptors in the adrenal gland. Dopaminergic ligands have been shown to modulate adrenocortical aldosterone biosynthesis and secretion as well as adrenomedullary catecholamine production and release. Using a combination of light microscopic immunochemistry and in situ amplification and hybridization, the present study sought to determine the site-specific expression of the recently cloned D1A receptor subtype in rat adrenal gland. Light microscopic immunohistochemistry was conducted using polyclonal antisera raised to the putative rat D1A receptor. Immunoreactive product was detected using an avidin-biotin immunoperoxidase method. D1A receptor messenger RNA (mRNA) was detected using a transcription-based isothermal in situ amplification and hybridization approach using receptor-specific mRNA oligonucleotide probes. The amplified product was localized using an alkaline phosphatase 4-nitro blue tetrazolium chloride/5-bromo-4-chloro-3-indolyl-phosphate technique. This combined experimental approach, using both receptor subtype-selective antibodies and oligonucleotide probes, allows for the site-specific localization of the D1A receptor subtype, which would otherwise not be possible with the pharmacological methods currently available. The D1A receptor protein and mRNA were expressed solely in the zona glomerulosa of the rat adrenal gland, with no signal evident in any of the other cortical layers or in the medulla. Such a distribution raises the possibility that the D1A receptor subtype could modulate, at least in part, some of the known effects of dopamine on aldosterone secretion.

Activation of phospholipase C by different effectors in rat placental cells

The present communication documents the accumulation of inositol phosphates in rat placental cells by fluoride as well as by vanadate. These findings suggest the existence of the phosphoinositide pathway and its modulation by a G-protein. A concomitant action of fluoride on phosphoinositide breakdown was also observed. As is often the case in intact cells from different organs, protein kinase C exerts a feedback regulatory control on this signalling system. Gonadotropin-releasing hormone (GnRH) also stimulated the accumulation of inositol phosphates in cultured cells but no effect could be detected in freshly isolated cells. Therefore, the phosphoinositide pathway seems to be involved in the mechanism of action of GnRH in rat placental cells.

Mechanisms involved in the interaction of dopamine with angiotensin II on aldosterone secretion in isolated and cultured rat adrenal glomerulosa cells

In a previous study, we have shown that freshly isolated glomerulosa cells possess dopamine (DA) receptors from both DA-1 and DA-2 subclasses, whereas in cultured conditions, cells exhibit dopamine receptors from the DA-1 subclass only. In the present work, we have studied the effect of DA on angiotensin-stimulated glomerulosa cells in these two experimental conditions. Our results demonstrate that in isolated cells, angiotensin II (AT) stimulates inositol phosphate accumulation, calcium influx and steroid secretion. Treatment with pertussis toxin completely blocks AT-stimulated steroid secretion and calcium influx and partially reduces inositol phosphate accumulation. DA alone has no effect on cAMP accumulation. However, in the presence of a specific DA-1 antagonist (SCH 23390), DA reduces intracellular cAMP content. Similarly, DA-like pertussis toxin produces the same inhibitory effects on AT-stimulated cells. The combined influence of DA and pertussis toxin is not additive suggesting that a 'Gi' GTP-binding protein is involved in the DA action. Specific DA antagonists indicate that these inhibitory processes are mediated through the DA-2 receptor subtype. DA may act by decreasing the intracellular calcium concentration since it reduces AT-stimulated Ca2+ influx and that both phospholipase C (PLC) and steroid accumulation are calcium dependent. Yet a direct inhibitory coupling between the DA-2 receptor and PLC may represent a second alternative since DA inhibitory effects are always present when calcium influx is artificially increased or decreased. In cultured cells, we observe an additive effect of DA and AT on aldosterone secretion, which is the result of additive interactions of the second messengers involved, namely cAMP for dopamine and inositol phosphates for angiotensin II. From these studies, we conclude that DA may exert a more versatile effect on aldosterone secretion than previously suspected.